useful: http://ehcp.net/?q=search/node/memory%20usage
there may be way to reduce ram usage, by optimizing some components.
such as: reduce apache worker count, disable unused mysql modules such as innodb,
remove some unused programs...
actually ehcp itsel does consume very little memory. however, other hosting software (webserver,dns etc.) consumes much of memory.
you need to optimize those software.

If you have little memory, I suggest you to use nginx instead of apache,
disable mysql innodb, remove all non-used modules, programs...